The increasing use and complexity of computer applications has led to a corresponding increase in data storage requirements. The costs associated with data storage are directly related to the efficiency and reliability of the data storage scheme employed. As such there is a continuing effort to improve data storage systems.
A file system is a scheme for storing and organizing electronic data with the goal of making such data easy to locate and access. In general, a file system consists of abstract data types implemented to effect the storage, organization, retrieval, and modification of the stored data. Typically, file systems used for large-scale data storage include one or more dedicated computers and software systems to manage data.
Conventional file systems include an underlying data storage device that offers access to an array of fixed-size blocks (e.g., 512-byte sectors). File system software organizes the blocks into files and directories and maintains associations between blocks and corresponding files.
File systems may be implemented as disk file systems in which data is stored to and accessed from a disk drive, which may be directly or indirectly connected to a computing system. File systems may also be implemented as network file systems in which data is stored and accessed over a network (e.g., a local area network (LAN)). A network file system is a distributed file system of files and directories located on remote computers within a network. Use of a network file system provides several advantages including, the management of remote files and directories as if they are local, mount referenced files systems, configuration of security options, management of mount properties and establish access permissions for hosts. Using a network file system, data may be stored and accessed by multiple computing systems concurrently. Network file systems may include, for example, NetWare Core Protocol (NCP) of Novell, Inc., Orem, Utah, the Common Internet File System (CIFS) developed by Microsoft Corporation of Redmond, Wash., and the UNIX-based Network File System (NFS) developed by Sun Microsystems, of Santa Clara, Calif.
One application for a file system, including a network file system, is to affect a backup storage scheme. That is, the continued increase in data storage has been accompanied by an increasing need to have an accurate record of the state of particular data stores at specified times. A backup of stored data may be created to affect recovery of data upon a catastrophic failure or to maintain a record of the state of the data at given times.
As noted above, a variety of schemes have been developed to provide more efficient data storage and such schemes are particularly applicable to data backup systems. This is because, depending upon the required backup frequency, enormous amounts of data are typically stored to provide reliable and updated backup data. This data must be stored efficiently to provide a cost-effective data backup scheme.
Network file systems, though providing numerous advantages in regard to storing and accessing data are often incompatible with techniques for improved storage efficiency and reliability. For example, typical network file systems (e.g., NFS) are stateless (i.e., for the NFS protocol, the state of interactions between the server and a client are not tracked or managed by the server during a session). So, if a client makes a request to a server, and after satisfying that request the server fails and is restarted, the server must be able to handle subsequent related requests from the client without needing to access state data that was lost when the server failed.
In general, this statelessness is achieved because each request has sufficient information to completely define the request. The required state is saved at the client and passed to the server with each request. In particular, the NFS protocol defines a data structure called a “file handle.” The file handle contains sufficient information to uniquely identify the file to be accessed. The advantage and purpose of a stateless server is to improve robustness by being able to continue file access in spite of the failure and restart of the file server.
However, statelessness means that when a file is transferred using the NFS protocol, it may be transferred as a number of fixed size blocks (e.g., 32 Kb blocks), which need not be in order.
Such fixed-size, unordered, data transmissions may be incompatible with data storage schemes that reduce or eliminate redundancies to improve storage efficiency and/or reliability.